The present invention relates to electroacoustic transducers of the piezoelectricity type for use with piezoelectric sounders, piezoelectric speakers, piezoelectric telephone receivers and the like, and more particularly to improvements of the structure of a piezoelectric electroacoustic transducer having a piezoelectric vibration plate housed within a resin casing assembled by ultrasonic welding techniques.
Conventionally, there have been well known piezoelectric electroacoustic transducers adaptable for use as piezoelectric sounders and piezoelectric speakers. Incidentally, in the piezoelectric electroacoustic transducers, it has been demanded to let them have dielectricity on the surfaces thereof in some applications. To this end, a piezoelectric electroacoustic transducer has been proposed which comes with a piezoelectric vibration plate as housed within the interior of its resin casing.
It should also be admitted that like other types of electronics parts or components, the piezoelectric electroacoustic transducer is also technically required to offer higher heat resistivity or thermal robustness. Accordingly, it is required to constitute the resin casing from synthetic resin materials with enhanced heat resistivity. However, such heat resistivity-enhanced synthetic resin materials are generally deficient in adhesionability, which would result in difficulty of employing a method of joining a plurality of resin casings together by bonding or adhesion techniques.
On the other hand, in the piezoelectric electroacoustic transducers, it has also been demanded to attain down-sizing and thickness reduction; in view of accommodating such demand, it is also difficult to provide special shapes and structures which require a plurality of resin casing components engaged with one another.
Then, as the method for enabling facilitation of down-sizing and thickness reduction while simultaneously enabling arrangement by use of synthetic resin materials with enhanced heat resistivity, a piezoelectric electroacoustic transducer has been proposed which includes its resin casing formed by causing two resin casing components to be adhered or bonded together by ultrasonic welding techniques for disposing a piezoelectric vibration plate within resultant resin casing (Published Unexamined Japanese Patent Application, or PUJPA, Nos. 62-109499 and 62-109500).
More specifically, the approach as disclosed in PUJPA No.62-109499 is such that a pair of casing components are subjected to ultrasonic welding while causing a circular or disk-like piezoelectric vibration plate to be held between the resin casing components with certain parts which hold the piezoelectric vibration plate therebetween being put into chosen liquid.
Alternatively, the approach disclosed in PUJPA No.62-109500 is such that while letting a disk-like piezoelectric vibration plate be sandwiched between a pair of resin casing components and at the same time causing the piezoelectric vibration plate to be supported by an elastic or resilient member for suppression of vibrations of the piezoelectric vibration plate, the resin casing components are ultrasonically welded at specific portions different from those portions whereat the piezoelectric vibration plate is sandwiched for suspension.
Ultrasonic welding is a method used in joining or bonding together certain synthetic resin materials with enhanced heat resistivity as stated supra; the same is also adaptable for use in reducing size and thickness because of its practicability without having to form any special engaging structures for such casing components.
However, with the ultrasonic welding, it can happen during welding that the disk-like piezoelectric vibration plate is self-destructible due to transmission of ultrasonic vibrations to the piezoelectric vibration plate side. Accordingly, in PUJPA No.62-109499, the piezoelectric vibration plate and parts of the resin casing components holding the piezoelectric vibration plate therebetween are fully put into chosen liquid while ultrasonically welding the resin casing components together at portions outside the liquid thereby eliminating occurrence of destruction of the piezoelectric vibration plate. Alternatively, in PUJPA No.62-109500, the disk-like piezoelectric vibration plate is forced to make contact with an associative elastic member for effectuation of ultrasonic welding while suppressing vibrations of the piezoelectric vibration plate in the way discussed previously.
In other words, while junction of the resin casing components using prior known ultrasonic welding techniques may advantageously serve to enable use of heat resistivity-excellent resin materials and also be suitable for facilitation of down-sizing and thickness reduction, such advantages do not come without accompanying a serious penalty of the need for time-consuming and troublesome works stated supra in order to prevent destruction of the piezoelectric vibration plate due to ultrasonic vibration transmission to the piezoelectric vibration plate.
It is therefore an object of the present invention to provide a piezoelectric electroacoustic transducer employing a resin casing structure essentially consisting of a plurality of resin casing components joined together by ultrasonic welding techniques with capability of easy assembly without the need for any complicated works such as putting into liquid certain part including the piezoelectric vibration plate and dumping vibration by forcing the piezoelectric vibration plate to come into direct contact with elastic or resilient members.
A piezoelectric electroacoustic transducer in accordance with the present invention as set forth in claim 1 is such that the piezoelectric electroacoustic transducer includes a piezoelectric vibration plate as housed in a casing structure essentially consisting of a plurality of resin casing parts or components bonded together by ultrasonic welding techniques, featured by employing a piezoelectric vibration plate which substantially resembles a rectangle in planar shape.
One advantage of the prescribed piezoelectric electroacoustic transducer lies in capability of suppressing destruction of the piezoelectric vibration plate because of the fact that the piezoelectric vibration plate is specifically designed to have a substantially rectangular planar shape, which in turn prevents or at least greatly suppresses vibration occurring during ultrasonic welding from being locally transferred to or xe2x80x9cconvergedxe2x80x9d at the center of the piezoelectric vibration plate, as will become apparent from a later description of some preferred embodiments of the invention.
More specifically, the aforesaid piezoelectric vibration plate is held by a plurality of resin casing components at the periphery thereof.
Preferably, the plurality of resin casing components are comprised of first and second resin casing components which are also arranged to substantially resemble a rectangle in planar shape, which in turn allows the piezoelectric vibration plate and resin casing components to be similar in planar shape to each other, thereby enabling facilitation of down-sizing or miniaturization of the piezoelectric electroacoustic transducer.
Additionally, in accordance with one specific aspect of the present invention, the piezoelectric vibration plate has a metal plate, a piezoelectric ceramic layer adhered to the metal plate, and electrodes formed on the opposite principal surfaces of the piezoelectric ceramic layer, wherein at least the metal plate is of a substantially rectangular planar shape. In this case the piezoelectric ceramic layer may be arranged to differ in planar shape from the metal platexe2x80x94that is, the layer may be of any other shapes such as a circular shapexe2x80x94or alternatively may be designed to have a rectangular planar shape in a way similar to that of the metal plate.
In accordance with a more limitative aspect of the present invention, the metal plate is provided as a metal plate which may function also as a corresponding associative terminalxe2x80x94say, xe2x80x9cdual functionalxe2x80x9d or xe2x80x9cterminal cofunctionalxe2x80x9d metalplate. In this case a lead terminal is further provided which is connected to specific one of the electrodes formed on the piezoelectric ceramic layer which one does not make contact with the metal plate while causing the terminal-cofunctional metal plate and the lead terminal to be externally elongated from the casing.
In accordance with another limitative aspect of the present invention, first and second lead members are in contact with the metal plate and the specific electrode electrically separated from the metal plate, respectively. These first and second lead members are to be externally taken out of the casing. The lead members may be constituted from either certain lead terminal made of metal plates or those lead wires with resiliency or flexibility.